1. Field of the Invention
This invention relates to a synchronous controller for controlling a servo motor for driving a robot, a machine tool, etc., with constant torque.
2. Description of the Related Art
FIG. 8 is a diagram to show the configuration of a torque constant synchronous control system for supplying a workpiece to a main spindle with a material supply machine in a related art. In the figure, numeral 31 denotes a workpiece, numeral 32 denotes a main spindle for rotating with the workpiece 32 fixed, numeral 33 denotes a main control servo motor, numeral 34 denotes a main controller, numeral 35 denotes a main control drive for performing position control of the main spindle 32 by the main control servo motor 33, numeral 36 denotes a material supply machine for supplying the workpiece 31 to the main spindle 32 and also giving a constant load to the workpiece 31 at the workpiece working time, numeral 37 denotes a torque control servo motor, numeral 38 denotes a torque controller, numeral 39 denotes a torque control drive for controlling the torque control servo motor 37 as constant torque so as to enable the material supply machine 36 to give a constant load to the workpiece 31, and numeral 40 denotes a numerical control for outputting a position command to the main control drive 35.
At the workpiece working time, the main control drive 35 performs axial position control of the main spindle 32 and the torque control drive 39 performs torque constant control so that the material supply machine 36 gives a constant load to the workpiece 31 during the workpiece working time.
In the torque constant synchronous control system in the related art, the main control drive 35 and the torque control drive 39 are controlled separately and as a result of the torque control drive 39 pressing the material supply machine 36 against the workpiece 31 under constant load by performing torque constant control, the main control drive 35 and the torque control drive 39 are operated synchronously.
FIG. 9 is a diagram to show the configuration of a complex lathe in a related art for working a workpiece in a state in which the workpiece is caught at both ends thereof, disclosed in JP-A-7-186007. In the figure, numeral 41 denotes a workpiece, numerals 42 and 43 denote face drivers touching the end face portions of the workpiece 41 in the vicinity of a rotation axis, numerals 44 and 45 denote head stocks on which a main spindle is mounted, numerals 46 and 47 denote Z-axis servo motors for driving the head stocks 44 and 45, numerals 48 and 49 denote servo amplifiers for driving the Z-axis servo motors 46 and 47, and numeral 50 denotes a numerical control (NC) for issuing a command to the servo amplifiers 48 and 49 and controlling the Z-axis servo motors 46 and 47.
The complex lathe in the related art is a lathe for working the workpiece 41 while synchronously operating the head stocks 44 and 45 with the workpiece 41 sandwiched at both ends between the face drivers 42 and 43 attached to the head stocks 44 and 45. At this time, the NC 50 performs torque constant synchronous control for synchronously operating the head stocks 44 and 45 with the workpiece 41 sandwiched therebetween at constant torque for at least either of the head stocks 44 and 45.
FIG. 10 is a block diagram of the complex lathe shown in FIG. 9. In FIG. 10, numerals 48 and 49 denote the servo motors, numeral 50 denotes the NC, numerals 51a and 51b denote parameters for setting data required for computing axis move data, etc., numerals 52a and 52b denote torque limit amounts for determining the torque amounts of the Z-axis servo motors 46 and 47, numerals 53a and 53b denote position feedback of the Z-axis servo motors 46 and 47 for driving the head stocks 44 and 45, numerals 54a and 54b denote press completion determination means for determining the head stocks 44 and 45 pressing against the workpiece 41, numerals 55a and 55b denote position command values for moving the head stocks 44 and 45 toward the workpiece 41, numerals 56a and 56b denote torque control means for controlling torque based on the torque limit amounts 52a and 52b, and numerals 57a and 57b denote power amplifiers for driving the Z-axis servo motors 46 and 47.
In the complex lathe in the related art, to hold a workpiece, the head stocks 44 and 45 are moved toward the workpiece 41 and the face drivers 42 and 43 come in contact with the workpiece 41 and if it is made impossible to move the head stock 44, 45 and the error amount from the position command value is increased, the torque control means 56a, 56b cuts the torque to the torque limit amount 52a, 52b and outputs the cut torque to the power amplifier 57a, 57b, thereby performing torque constant control.
In a state in which the torque is output so as to become the torque limit amount 52a, 52b, when the press completion amount becomes less than (position command value 55a--position feedback 53a) or the press completion amount becomes less than (position command value 55b--position feedback 53b), the press completion determination means 54a, 54b determines the pressing to be complete, and stops increasing the position command value.
The complex lathe in the related art is a lathe for sandwiching the workpiece 41 between the head stocks 44 and 45 at constant torque for holding the workpiece 41 and working the workpiece 41 in the state as in the above-described sequence.
In the torque constant synchronous control system in the related art shown in FIG. 8, as a result of the torque control drive 39 pressing the material supply machine 36 against the workpiece 31 under constant load by performing torque constant control, the main control drive 35 and the torque control drive 39 are operated synchronously. Thus, the torque constant synchronous control system cannot be used in applications wherein the torque control drive 39 cannot follow the motion of the main control drive 35, for example, applications at the rapid acceleration or deceleration time or when excessive backlash exists because the workpiece 31 may fall out from the material supply machine 36 because of insufficient press load or may become deformed because of excessive press load; this is a problem of the torque constant synchronous control system.
To avoid torque instability of the press load caused by the fact that the torque control drive 39 cannot follow the motion of the main control drive 35, a method of performing only torque constant control at the stop time and inputting a position command as a synchronous pattern from an external control section and accomplishing synchronous operation under position control at the moving time may be adopted. However, any of the following:
a. backlash caused by the mechanical structure of the torque control drive 39, the material supply machine 36, PA1 b. torque variation caused by position droop variation caused by a warp in the workpiece 31, etc., PA1 c. press load instability caused by counter force of synchronous shafts, PA1 d. position droop at the torque constant control time, or the like may induce mechanical vibration because of excessive output of a torque command at the position control switch time, and it is difficult to perform stable and high-accuracy synchronous control; this is a problem.
Further, in the complex lathe in the related art shown in FIGS. 9 and 10, torque constant control of pressing with the torque limit amount set is executed and acceleration/deceleration based on acceleration/deceleration torque larger than the setup torque limit amount at the torque constant synchronous control time cannot be executed, thus the complex lathe cannot be used in applications wherein rapid load variation exists; this is a problem.